> Webs from woodland and zoo show eDNA from native and non-native fauna, respectively
It does not matter, the effect on the enclosure is the problem.
They compared a web found in native woodlands to a web in a zoo enclosure to demonstrate the potential to detect local animal populations. The zoo had more species because it's a zoo. They didn't limit the study to only zoo-bound webs as you seem to be suggesting.
This will be really neat when we have Spide-Spun-Space-Sensors whereby a planet it cluster-bombed with sensor-balls with a special spider-silk-style web which can grab DNA, but onboard sequence it... and report back to the orbiting drone before self destruction.
You can just vacuum and filter the air for dna
Wow, crime scene DNA-Devil: Here is a simple attempt at an sensor gun to dirt-devil up crimescene DNA powered by SyDNAr sensors (TM):